Grain structure analysis and effect on electromigration reliability in nanoscale Cu interconnects

The grain structure in Cu interconnects of the 45 nm node was analyzed to yield grain orientation and boundary characteristics using a high-resolution electron diffraction technique. A dominant sidewall growth of {111} grains was observed, reflecting the importance of interfacial energy in controlling grain growth below 70 nm linewidth. The grain structure was used to identify flux divergent sites for void formation under electromigration (EM) and to analyze the effect on EM statistics for Cu lines with CoWP capping using a microstructure-based model. This analysis established a correlation between the microstructure of Cu nanolines, void formation kinetics, and EM statistics.